Human Molecular Genetics Advance Access originally published online on March 6, 2007
Human Molecular Genetics 2007 16(7):837-847; doi:10.1093/hmg/ddm029
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Published by Oxford University Press 2007
Production of lysophosphatidylcholine by cPLA2 in the brain of mice lacking PPT1 is a signal for phagocyte infiltration
1 Section on Developmental Genetics, Heritable Disorders Branch, National Institute of Child Health and Human development, The National Institutes of Health, Building 10, Room 9D42, 10 Center Drive, Bethesda, MD 20892-1830, USA, 2 Department of Cancer Biology, The Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Avenue, Cleveland, OH 44195, USA and 3 Walter Reed Army Institute of Research, Silver Spring, MD 20910-7500, USA
* To whom correspondence should be addressed at: Tel: +1 3014967213; Fax: +1 3014026632; Email: mukherja{at}exchange.nih.gov
Received December 12, 2006; Revised February 12, 2007; Accepted February 12, 2007
In the majority of neurodegenerative storage disorders, neuronal death in the brain is followed by infiltration of phagocytic cells (e.g. activated microglia, astroglia and macrophages) for the efficient removal of cell corpses. However, it is increasingly evident that these phagocytes may also cause death of adjoining viable neurons contributing to rapid progression of neurodegeneration. Infantile neuronal ceroid lipofuscinosis (INCL) is a devastating, neurodegenerative, lysosomal storage disorder caused by inactivating mutations in the palmitoyl-protein thioesterase-1 (PPT1) gene. PPT1 catalyzes the cleavage of thioester linkages in S-acylated (palmitoylated) proteins and its deficiency leads to abnormal accumulation of thioesterified polypeptides (ceroid) in lysosomes causing INCL pathogenesis. PPT1-knockout (PPT1-KO) mice mimic the clinical and pathological features of human INCL including rapid neuronal death by apoptosis and phagocyte infiltration. We previously reported that in PPT1-KO mice, the neurons undergo endoplasmic reticulum stress activating unfolded protein response, which mediates caspase-12 activation and apoptosis. However, the molecular mechanism(s) by which the phagocytic cells are recruited in the PPT1-KO mouse brain remains poorly understood. We report here that increased production of lysophosphatidylcholine (LPC), catalyzed by the activation of cytosolic phospholipase A2 (cPLA2) in the PPT1-KO mouse brain, is a ‘lipid signal’ for phagocyte recruitment. We also report that an age-dependent increase in LPC levels in the PPT1-KO mouse brain positively correlates with elevated expression of the genes characteristically associated with phagocytes. We propose that increased cPLA2-catalyzed LPC production in the brain is at least one of the mechanisms that mediate phagocyte infiltration contributing to INCL neuropathology.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.
Present address: Department of Obstetrics and Gynecology, Indiana University School of Medicine, Indianapolis, IN 46202, USA.